WASHINGTON (AFP) - Oil giant BP, with Swedish chairman Carl-Henric Svanberg, blames rig owner Transocean for the giant oil spill that threatens US shores.

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Oil industry executives traded blame Tuesday for the Gulf of Mexico oil spill as US lawmakers grilled them over the giant slick threatening environmental and economic calamity.

Key executives from BP, Halliburton and Transocean faced off at two congressional hearings examining the April 20 explosion on the Deepwater Horizon rig, which killed 11 workers and has led to one of the worst spills in US history.

Operator BP said rig owner Transocean, the world's largest offshore drilling contractor, was responsible for the failure of a giant valve system to stop the blast.

"Why did Transocean's blowout preventer, the key failsafe mechanism, fail to shut in the well and release the rig?" BP's America chief Lamar McKay testified.

Transocean chief executive Steven Newman passed the buck back, saying: "All offshore oil and gas production projects begin and end with the operator."

Newman also pointed the finger at Halliburton, saying the US oil services behemoth was responsible for the cement work that may have failed to seal the exploratory well correctly.

Halliburton's chief safety officer Tim Probert said BP was ultimately responsible for all of the work done on the rig and that his firm had met the British energy giant's instructions and industry practice.

"I hear one message. And the message is, don't blame me," the exasperated Republican Senator John Barrasso told the Energy and Natural Resources Committee hearing. "Well, shifting this blame does not get us very far."

While willing to display their anger that no one would step up and acknowledge being at fault, senators were reluctant to be too hard on an industry on which oil-thirsty America is so dependent.

"Blocking future offshore exploration only means we will import more from foreign countries," admitted Barrasso.

But the ranking Republican on the committee, Senator Lisa Murkowski, suggested the future of offshore drilling was at stake if the industry failed to convince the public their activities were safe.

"Not only will BP not be out there, but the Transoceans won't be there... and the Halliburtons won't be there."

Moments before the hearing began, demonstrators took aim at BP, some with black teardrops painted on their faces in quiet protest, others calling out "BP kills wildlife, BP kills people, BP kills the planet."

McKay said during his testimony on Tuesday that BP would pay "all legitimate claims" of economic damages, well over a 75-million-dollar legal ceiling.

BP has accepted responsibility for the clean-up and is leading frantic efforts to stop an estimated 210,000 gallons of oil from spewing into the sea each day.

It lowered a giant dome over the main leak on Friday but by Sunday this had become clogged with ice crystals and was unable to function as intended as a funnel to divert the leaking oil up to a waiting tanker on the surface.

BP plans to make a second attempt this week with a smaller version, dubbed the "top hat," which it will lower onto the ruptured pipe nearly a mile (1,500 meters) down on the seabed.

BP began drilling a relief well on May 2 that could divert the flow until the well is permanently sealed, but this may not be ready until August so engineers are furiously searching for alternatives.

US military flights from across the United States began arriving Tuesday in Louisiana laden with BP and Department of Defense stock equipment to fend of the incoming oil spill in the Gulf of Mexico.

The first three of 10 C-17 flights bringing supplies from Alaska and other states landed at Naval Air Station Joint Reserve Base in Belle Chasse just outside New Orleans, bringing in a total of 150,000 feet (45,700 meters) of BP and Navy boom.

Other than a variety of boom materials, floats, skimming equipment and other materials are also being brought in to be taken staging areas in the effort to halt the the spill reaching the fragile US wetlands along the Gulf coast.

As efforts to contain the leak grow more desperate, an oil slick the size of a small country has developed off Louisiana, sending large expanses of sheen near vital shipping lanes and encircling ecologically fragile nature reserves.

Louisiana's 2.4 billion dollar fishing industry is already being hit by a partial ban and animals are at risk in a region that is a major migratory spot for rare birds and contains vital spawning grounds for fish, shrimp and crabs.

President Barack Obama has dispatched a fresh delegation of officials led by Energy Secretary Steven Chu to meet this week with BP representatives in Houston, Texas.

His administration also announced plans Tuesday to split the Minerals Management Service (MMS) into two separate parts: one to regulate the industry, and another to provide drilling leases and collect federal royalties.

The probe co-chaired by the US Coast Guard and the MMS, began with a moment of silence for the 11 dead workers.